Electrophotographic apparatus

ABSTRACT

A photocopying apparatus which comprises supply means for supplying a predetermined quantity of concentrated developing agent to carrier liquid at a predetermined time interval, and measuring means for continuously measuring the concentration of the developing liquid. The measuring means controls said supply means so that the supply means supplies such measured quantity of concentrated developing agent to the carrier liquid only during predetermined time intervals and then only where the developing liquid has lower than a predetermined value of concentration. The carrier liquid is independently supplied in a quantity equal to the consumption of the carrier liquid, whereby constant concentration of the developing solution is maintained.

United? States Patent Knechtel et al.

1 1 Oct. 24, 1972 1541 ELECTROPHOTOGRAPHIC APPARATUS [72] Inventors:Wilhelm Josef Knechtel, Rodheim; Detlef Schaifer, Wetzlar, both ofGermany [73] Assignee: lanon Kabushiki Kaisha, Tokyo,

Japan [22] Filed: July 13, 1970 [21] Appl. No.: 54,336

[30] Foreign Application Priority'Data July 16, 1969 Germany ..P 19 36167.2

52] u.s.c1. ..137/93,137/5,l37/88 51 1m; 01. .;..G05d 11/08- 58]FieldofSearch ..137/93,ss,4,5,s,9

[56] References Cited UNITED STATES PATENTS 3,494,328 2/1970 Maloney..137/93 3,526,338 9/1970 Goodrich ..137/93 3,548,855 12/1970 Fathauer..137/93 3,195,551 7/1965 Russell ..137/5 1/1967 Kolb ..l37/93 3,217,72911/1965 Ballestra ..l37/93 3,223,108 12/1965 .Martz ..l37/93 PrimaryExamineF-M. Cary Nelson Assistant Examiner-William H. WrightAttorney-Watson, Leavenworth and Kelton [57] ABSTRACT A photocopyingapparatus which comprises supply means for supplying a predeterminedquantity of concentrated developing agent to carrier liquid at apredetermined time-interval, and measuring means for continuouslymeasuring the concentration of the developing liquid. The measuringmeans controls said supply means so that the supply means supplies suchmeasured quantity of concentrated developing agent to the carrierliquidonly during predetermined time intervals and then only where thedeveloping liquid has lower than a predetermined value of concentration.The carrier liquid is independently supplied in a quantity equal to theconsumption of the carrier liquid, whereby constant concentration of thedeveloping solution is maintained.

11 Claims, 1 Drawing Figure PATENTEI] MIT 24 I97? 3. 699 ,992

1 ELECTROPHOTOGRAPHIC APPARATUS BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to photocopying apparatus fordeveloping an electrostatic image which includes a container containingdeveloping liquid and measuring means associated therewith for automaticcontrol of developing liquid concentration.

2. Description of the Prior Art In the production of copy, it-is knownthat a developing agent, such as toner, must be taken in a variablequantity from carrier liquid in accordance with the contrast to beprovided on the surface of the copy.

On the other hand, the carrier liquid is constantly removed from thedeveloping solution container, and in this case the amount of carrierliquid removed is related to the size of copying paper sheet passingthrough the apparatus, because the liquid sticks to the surface of thepaper sheet. Therefore, the toner concentration in. the carrier liquidis continuously varying and this often results in unsatisfactory copies.To prevent this, there has been provided measuring means for constantlymeasuring the concentration of the developing agent in the carrierliquid and, if required, supplying developing agent in concentrated formto the carrier liquid.

In apparatus of the known type, a great time delay occurs between themeasurement and the subsequent toner supply control, with a result thatthe concentration of the developing solution is greatly varied even ifit is continuously monitored. In such apparatus, the developing liquidis supplied to a measuring station forming a part of a Wheatstonebridge. As the concentration varies, the photoresistance in the bridgevaries in magnitude. The current driving a pump flow in the bridge anddeveloping agent in concentrated form is supplied from a reservoir intothe container by the pump. in such apparatus, the concentrateddeveloping agent is supplied until the measuring station detects a newlevel of concentration. At this stage, saturation must apparently havebecome excessive. On the other hand, the supply means is of courseresponsive only when a low concentration initially appearingin thecontainer is detected at the measuring station.

- SUMMARY OF THE-INVENTION the carrier liquid at said time interval onlywhen the developing solution has lower than a predetermined value oftoner concentration and that said supply means is maintained inoperativewhen the developing solution exceeds or reaches said predetermined valueof concentratiom'said carrier liquid for diluting the concentrateddeveloping agent being independently supplied in a quantity equal to theconsumption of the developing agent.

Su'ch method of control has, on the one hand, the advantage that thequantity of liquid in the container can always be maintained constant bythe supply of carrier liquid. Such supply means is known as the chickenwatering place.

Thus, a small quantity of concentrated toner liquid is supplied at atime interval which may be 30 seconds 7 only when the concentration ofthe liquid in the container becomes lower than a reference value,whereby the concentration is maintained constant, because the timeinterval at which the measured quantity is supplied provides asufficient length of time to allow, on the one hand, the concentrateddeveloping agent to be well mixed with the carrier liquid by a stirrerin the container and-to allow, on the other hand, a good mixture to besupplied to the measuring station.

The concentration is continuously measured by photoconductive means, forexample. For this purpose, a pump continuously takes solution out of thedeveloper container and supplies it to a transparent tube having asource of light, and a photocell mounted forwardly and rearwardlythereof respectively.

The supply of developing agent may conveniently be effected by ameasuring pump which is operated at a controlled time interval andsupplies concentrated developing agent from a reservoir to thedeveloping solution container.

In another form of the present invention, the measuring pump isconnected to an AND gate, which is controlled by the measuring means onthe one hand and by a pulse generator on the other hand. A Schmitttrigger may preferably be provided between the measuring means and theAND gate.

When the concentration is reduced to cause the voltage in the photocellto exceed a value determined by the Schmitt trigger input threshold, thetrigger applies an enabling signal to the AND gate. When a pulse iscoincidentally applied to the gate from a pulse generator, the measuringpump is operated, preferably by an operational amplifier. The operationof the measuring pump only continues for a short time, because the pulsegenerator applies a short pulse, say, of one-tenth second, to the ANDgate. At the moment when the pulse has passed through the gate, thepulse generator discontinues applying a pulse to the AND gate. As aresult, the AND gate does not pass any signal, whereby the measuringpump is no longer operated. This is also the input case where thevoltage of the Schmitt trigger is low because of sufficientconcentration of developing agent in solution and the Schmitt triggerdoes not apply an enabling to the AND gate. In this case, no pulse isapplied from the AND gate to the measuring pump in spite of the presenceof pulses produced by the pulse generator. When the Schmitt trigger doesapply an enabling signal to the AND gate, the measuring pump is againoperated for a short time by coincident pulse from the pulse generator.

The pulsegenerator can be controlled in an ordinary manner so thatpulses can be successively generated at a time interval of 3 for 30seconds. The time interval can be adjusted to each apparatus in use inaccordance with the time required for the circulation of developingliquid and the time required for mixing.

The apparatus according to the present invention accu'rately operatesand maintains theconcentration substantially constant.

in a further form of the present invention, the circulation means andthe pump for constantly supplying liquid to the measuring-portion aretime-controlled so that developing liquid may be circulated at a timeinterval of 2'0 to 30 minuteshfor example, when the apparatus-is notoperated but is in standby position. Thus,

the apparatus is always ready for operation even after it has not beenused. fora longtime. If such circulation does not take place, theconcentrated toner will be deposited on the bottom of the developingsolution container. In this case, the apparatus-will not be ready foroperation until concentrated developing agent is newly mixed-withcarrier liquid. Furthermore, the

. separation of the concentrated toner will prevent the mixed toner frombeing supplied to the measuring sta-' tion when the apparatus isstarted, while either the concentrated toner itself or the carrierliquid will. besupplied to the measuring station, thus resulting in awrong abling O-signal to-the AND gate 9, Thus, no L-signal is applied tothe operation amplifier 11 in the last-mentioned instance even if thepulse generator 10 then applies an L-signal to the AND gate. The pump 12sup- "plies concentrated toner from a reservoir 13 through a imagescomprising:

measurement which would dangerously hamper thesupply of concentratedtoner.

- The present invention will now be described way of examplewithreference to the accompanying drawn A BRIEF DESCRIPTION oF THE DRAWINGThe drawing diagrammatically shows an embodiment of the presentinvention.

7 DESCRIPTION OF THE PREFERRED EMBODIMENTS 1 Referring to the drawing,developing solution 3 in a developer container 1 is pumped out by a pump2 and forced through a transparent tube 4 into a conduit 5 and againinto the container 1.

"A source of light 6 is provided to illuminate the transparent tube 4.When the developing solution passing through the tube 4 has a highconcentration of developing agent, a photocell 7 receives a smallquantity-of light and, when theconcentration is low, receives a largequantity of light. A voltage produced in the photocell 7 isapplied as aninput output signal to a Schmitt trigger 8. When the photocell 7produces a high voltage, i.e., when the concentration of the developingliquid is low, the trigger produces an output signal L. An output signal0 is produced in the opposite case.

- The trigger output signal is applied to' an AND gate 9. The AND gate 9is in turn connected to a pulse generator 10, whichselectively generatespulses (L-- two coincident Lsignals. An O-signal is applied to the ANDgatebetween each pair of successive pulses generated by the pulsegenerator. In this case no pulse is applied to the operationamplifier11. This also holds true at any time when the Schmitt trigger applies adis a. a tank containing developing solution comprising carrier liquidadmixed with developing agent; bgmeans circulating said developingsolution; c. sensing means generating first output signalsduring'operationof saidcirculating means, said first output signalsbeing indicative of the concentra- 'tion of developing agent in v tion;I v

d. means generating time spaced signals during operation of saidcirculating means;

e. means receiving saidfirst output signals and said time-spaced signalsand operatively responsive thereto to generate second output signalsexclu sively upon the concurrent occurrence of said time-spaced signalsand firstoutput signals indicative of developing agent concentration ofmagnitude less than a preselected-magnitude; and

f. developing agent supply means operatively responsive .to said secondoutput signals to supply said developing soludeveloping agent to saidtank during the time exv tents of said second output signals.

2. The apparatus claimed in claim 1 wherein said developing agent supplymeans comprises a container containing concentrated developing agent,conduit means connecting said container and said tank and a pumpdisposed in said conduit means and operatively responsive to said secondoutput signals.

3. The apparatus claimed in claim 2 wherein said second output signalgenerating means includes a coincidence circuit receivingv said firstoutput signals and said time-spaced signals. 1

4. Apparatus for use in developing electrostatic images comprising:

a. a tank containing developing solution comprising carrier liquidadmixed with developing agent;

b. means circulating said developing solution;

c. sensing means generating first output signals during operation ofsaid circulating means, said first output signals being indicative ofthe concentra-' tion of developing agent in said developing solu-. tion;

d. means generating second output signals at predetermined periodsduring operation of said circulating means exclusively upon theoccurrence during said periods of first output signals indicative ofdeveloping agent concentration of magnitude less than a preselectedmagnitude, sad second output signal generating means comprising firstcircuit means generating pulses time-spaced from one another and each oftime extent defining a one of said predetermined periods and secondcircuit meansincluding a coincidence circuit operatively responsive tosaid pulses and said first output signals, said coincidence circuitproviding output signals constituting said second output signals; and

e. developing agent supply means operatively responsive to said secondoutput signals to supply developing agent to said tank during the timeextents of said second output signals.

5. The apparatus claimed in claim 3 including a voltage-sensitivebistable circuit connected between said sensing means and saidcoincidence circuit.

6. The apparatus claimed in claim 5 wherein said coincidence circuitcomprises an AND gate receiving a first input from said bistable circuitand a second input from said means generating said time-spaced signals.

7. The apparatus claimed in claim 6 further including an operationalamplifier receiving said AND gate output signal, said amplifier outputsignals constituting said second output signals.

8. The apparatus claimed in claim 11 wherein said circulating meansincludes a conduit and wherein said sensing means includes a lightsource and a photocell disposed in opposing relation in said conduit.

9. The apparatus claimed in claim 11 further including a rotatingstirrer disposed in said tank.

10. The apparatus claimed in claim 8 wherein said circulating meansfurther includes a pump connecting said tank and said conduit.

11. The apparatus claimed in claim 8 wherein said conduit comprises atransparent section, said light source and said photocell being mountedon said transparent conduit section.

1. Apparatus for use in developing electrostatic images comprising: a. atank containing developing solution comprising carrier liquid admixedwith developing agent; b. means circulating said developing solution; c.sensing means generating first output signals during operation of saidcirculating means, said first outpuT signals being indicative of theconcentration of developing agent in said developing solution; d. meansgenerating time-spaced signals during operation of said circulatingmeans; e. means receiving said first output signals and said timespacedsignals and operatively responsive thereto to generate second outputsignals exclusively upon the concurrent occurrence of said time-spacedsignals and first output signals indicative of developing agentconcentration of magnitude less than a preselected magnitude; and f.developing agent supply means operatively responsive to said secondoutput signals to supply developing agent to said tank during the timeextents of said second output signals.
 2. The apparatus claimed in claim1 wherein said developing agent supply means comprises a containercontaining concentrated developing agent, conduit means connecting saidcontainer and said tank and a pump disposed in said conduit means andoperatively responsive to said second output signals.
 3. The apparatusclaimed in claim 2 wherein said second output signal generating meansincludes a coincidence circuit receiving said first output signals andsaid time-spaced signals.
 4. Apparatus for use in developingelectrostatic images comprising: a. a tank containing developingsolution comprising carrier liquid admixed with developing agent; b.means circulating said developing solution; c. sensing means generatingfirst output signals during operation of said circulating means, saidfirst output signals being indicative of the concentration of developingagent in said developing solution; d. means generating second outputsignals at predetermined periods during operation of said circulatingmeans exclusively upon the occurrence during said periods of firstoutput signals indicative of developing agent concentration of magnitudeless than a preselected magnitude, sad second output signal generatingmeans comprising first circuit means generating pulses time-spaced fromone another and each of time extent defining a one of said predeterminedperiods and second circuit means including a coincidence circuitoperatively responsive to said pulses and said first output signals,said coincidence circuit providing output signals constituting saidsecond output signals; and e. developing agent supply means operativelyresponsive to said second output signals to supply developing agent tosaid tank during the time extents of said second output signals.
 5. Theapparatus claimed in claim 3 including a voltage-sensitive bistablecircuit connected between said sensing means and said coincidencecircuit.
 6. The apparatus claimed in claim 5 wherein said coincidencecircuit comprises an AND gate receiving a first input from said bistablecircuit and a second input from said means generating said time-spacedsignals.
 7. The apparatus claimed in claim 6 further including anoperational amplifier receiving said AND gate output signal, saidamplifier output signals constituting said second output signals.
 8. Theapparatus claimed in claim 1 wherein said circulating means includes aconduit and wherein said sensing means includes a light source and aphotocell disposed in opposing relation in said conduit.
 9. Theapparatus claimed in claim 1 further including a rotating stirrerdisposed in said tank.
 10. The apparatus claimed in claim 8 wherein saidcirculating means further includes a pump connecting said tank and saidconduit.
 11. The apparatus claimed in claim 8 wherein said conduitcomprises a transparent section, said light source and said photocellbeing mounted on said transparent conduit section.